A sketch of the central nervous system and its origins
G. E. Schneider 2014
Part 3: Specializations in the evolving CNS; introduction to connection patterns
MIT
9.14
Class 6
Interlude:
Some specializations involving head receptors and brain expansions
with questions on book chapter 6
1
X
Examples of evolution of non-olfactory
sensory specializations (Most, if not all, led
to expansions of brain representations)
• Electro-reception in some fish  Cerebellar expansion
in Mormyrid fish
• Infra-red detectors in the pit vipers  specialized trigeminal nerve (5th cranial nerve) inputs
• Echo-location in bats and porpoises  specialized auditory system
• High visual acuity and learned object recognition in primates 
expansion of visual cortical areas
• Vibrissal sensitivity in rodents specialized somatosensory system
2
Questions, chapter 6
1. What cranial nerves carry information from electroreceptors
in certain fish? Why is electroreception so useful for these
fish? Why is their visual sense not adequate?
Lateral line nerves (cranial nerves, up to six of them)
3
Courtesy of MIT Press. Used with permission.
Schneider, G. E. Brain structure and its Origins: In the Development and in
Evolution of Behavior and the Mind. MIT Press, 2014. ISBN: 9780262026734.
4
Questions, chapter 6
2. No placental mammals have electrosensory abilities, but
one non-placental mammal does have such an ability.
Which one? How are this animal’s electroreceptive inputs
different from electrosensory fish in the cranial nerves
involved?
Duck-billed platypus -- a monotreme.
A branch of the trigeminal nerve (the 5th cranial
nerve) that innervates the bill.
5
Questions, chapter 6
3. Another sense that is not highly developed in mammals is
infra-red detection. In what animals is this particularly
important? Which cranial nerve is involved?
Next
6
Ophthalmic Branch
Mandibular Branch
Maxillary Branch
Sensory (Infrared) pit
Image by MIT OpenCourseWare.
Rattlesnake trigeminal nerve: innervation of a specialized distance sense
7
Questions, chapter 6
4. Bats are not the only mammal with echolocation ability. In
what other mammal is it found? Which cranial nerve is
greatly enlarged in that animal?
8th nerve
Next slide
8
ECHOLOCATING BAT
DOLPHIN
IC
IC
{
SC
{
SC
1 cm
2 mm
IBEX
SC
IC
IC
{
Tarsier: a
prosimian
primate
SC
1 mm
{
Ibex: a
wild goat
TARSIER
5 cm
Image by MIT OpenCourseWare.
From Georg Striedter (2005), p. 166
Midbrain roof: the colliculi in four mammals
IC = inferior colliculus. SC = superior colliculus
9
Questions, chapter 6
5. What is a brain manifestation of the specialization of
primates for vision?
10
Visual areas, owl monkey neocortex
M
V2
MT
V1
LATERAL VIEW
Image by MIT OpenCourseWare.
11
Questions, chapter 6
6. What is a brain manifestation of the specialization of small
rodents for using their vibrissae (whiskers) so well?
Describe other somatosensory specializations in some
mammals.
12
Three successive tangential
sections of rat hemisphere,
Nissl stain, showing the
“barrel fields”:
Figure removed due to copyright restrictions.
Please see course textbook or:
Woolsey, Thomas A., and Hendrik Van der Loos. "The Structural Organization of Layer IV in
the Somatosensory Region (SI) of Mouse Cerebral Cortex: The Description of a Cortical Field
Composed of Discrete Cytoarchitectonic Units." Brain Research 17, no. 2 (1970): 205-42.
Each barrel represents
one whisker
13
Figure removed due to copyright restrictions.
Please see course textbook.
Schneider, G. E. Brain Structure and its Origins: In the Development and in
Evolution of Behavior and the Mind. MIT Press, 2014. ISBN:9780262026734.
Barrel field in 4-day-old rat: axons from thalamus
Fig.6-5b
14
Other somatosensory specializations
• The hand in apes, raccoons and, especially, humans (with high tactile acuity & fine motor control)
expansions of somatic sensory-motor cortex and of cerebellar hemispheres [See next slide]
• Prehensile tail in spider monkey  expanded tail representations in sensory & motor neocortex
15
Somatosensory neocortex, hand area of two species
A separate
gyrus for
each digit
in raccoon
Image by MIT OpenCourseWare.
16
Questions, chapter 6
7. What may be a brain manifestation of the human
abilities for complex social interactions?
8. What is a striking specialization (specific
function unclear) in the brain of the Echidna (the
spiny anteater of Australia)?
17
Other behavioral specializations
• Elaborate social organization in primates, with
planning and problem solving expanded
prefrontal neocortical areas
18
Brain of an Echidna, the spiny anteater—an Australian monotreme showing an enlarged prefrontal neocortex
Courtesy of MIT Press. Used with permission.
Fig. 6-7
Schneider, G. E. Brain structure and its Origins: In the Development and in
Evolution of Behavior and the Mind. MIT Press, 2014. ISBN: 9780262026734.
19
Questions, chapter 6
9. What other specializations might have noticeable
brain manifestations? Try to think of something
not mentioned in chapter 6.
Class discussion:
Humans with specially developed abilities may have greater
development of certain brain areas. Examples: blind people can
have some echolocation abilities; London taxi drivers have
unusually large parietal cortical areas -- were they like that from
early development, or did these areas enlarge as a result of
repeated activity?
Specialized noses: the star-nosed mole; the elephant's trunk
20
Class session 6 was organized in 2 parts:
1.
Some specializations involving head receptors and brain
expansions, which correspond with Chapter 6 of the course
textbook and were covered in the previous slides.
2.
Overview of forebrain structures in vertebrates and an introduction
to the neocortex, which correspond with Chapter 7 of the course
textbook and are covered in the proceeding slides.
21
A sketch of the central nervous system and its origins
G. E. Schneider 2014
Part 3: Specializations in the evolving CNS;
introduction to connection patterns
MIT 9.14 Class 6b
Overview of forebrain structures in vertebrates; neocortex introduced
Questions on chapter 7 of book
22
Functional overview of cephalic structures
• What can an animal do without a forebrain? Behavior of chronic decerebrate cats, rats and pigeons. –Decerebration: removal of cerebral hemispheres
(surgical removal of all or most of the forebrain)
• Contributions of forebrain components
–Diencephalon (‘tweenbrain)
–Corpus striatum
–“Limbic” system
–Neocortex
23
Sketch of a pre-mammalian brain
Courtesy of MIT Press. Used with permission.
Schneider, G. E. Brain structure and its Origins: In the Development and in
Evolution of Behavior and the Mind. MIT Press, 2014. ISBN: 9780262026734.
Note: Almost all axons were much more widely branching than shown
in this schematic. Dendrites, also highly branched, are omitted
24
Questions, chapter 7
1. What is the major reason for the very
different effects of forebrain removal in cats
and rats?
the number of connections disrupted
25
Questions, chapter 7
2. Why was forced feeding required to keep decerebrate cats alive after the surgery?
They had lost normal hunger motivation.
26
Cats: decerebration effects
• See the conclusion of Bard & Macht (1958) about
reflex animals.
• What can such an animal actually do?
• Is it able to learn?
Bard & Macht, 1958; Emmers, Chun & Wang, 1965; Markel & Adam, 1965.
27
Decerebrate cat behavior, 1
• Anosmic and blind, with loss of cranial nerves 1 and 2
• Failure to eat spontaneously; licking & chewing
responses to food placed in the mouth (Forced feeding
keeps cats alive.)
• Failure to groom
• No spontaneous sexual or other social behavior; sexual
reflexes elicited by genital stimulation
28
Decerebrate cat behavior, 2
• Good standing, sitting, righting, walking, but
abnormal posture & gait; failure to reposition limbs
• Rage responses—e.g., to tail pinching—but failure
to bite or strike out
• Autonomic responses: piloerection,
thermoregulatory responses but only to extreme
temperatures unless hypothalamus left attached
- A hypothalamic island was usually spared because of
need for crucial visceral regulation, e.g., water balance.
The island was attached to the posterior pituitary.
• Minimal learning: Conditioned eye blink or
respiratory changes occur but there is a rapid loss of
the learning.
29
Questions, chapter 7
3. Describe the behavior that shows how a cat
without a forebrain shows no hunger
motivation and yet will eat when food is
placed in its mouth.
Eating reflexes
30
Chronic decerebrate rats (Woods, 1964)
• Similar to the decerebrate cats in many respects, but more rapid
recovery of righting reflexes and locomotion
• More eating & drinking responses, but no seeking of food
(hence, the damage was fatal without special interventions)
• Grooming occurred. (Thus, they showed a “series of reflexes” –
more accurately described as a fixed action pattern.)
• Typical rodent defensive behavior (vocalizations, escape
attempts, clawing & biting)
• Some auditory localization in space (shown by orienting towards
sounds)
31
Questions, chapter 7
4. Is it true to say that the cat’s forebrain has
“taken over” more functions than the rat’s
forebrain? Is this the best way to describe
the results of experiments?
This would imply that there is a qualitative difference between
the species. It is more accurate to describe the results as
indicating quantitative differences.
32
Questions, chapter 7
5. What are some of the unlearned behavior
patterns exhibited by pigeons that had
suffered a disconnection of the forebrain
from the midbrain, except for the
connections from the eyes to the dorsal
midbrain.
Next slide
33
Pigeons with forebrain removed, sparing the
optic tracts (Visser & Rademacher, 1935, 1937)
• They showed a basic repertoire of “unlearned”
reactions:
– Thrown into the air, they flew, avoided vertical sticks, and
landed on horizontal sticks.
– But they also landed on the backs of dogs and cats!
• They lost many more complicated behavior patterns that seemed to depend to some degree on learning.
34
Pigeons with forebrain removed: Learning?
• Have they lost learned behavior and retained
unlearned behavior? – This is too extreme, although they did lose many learned
responses.
– Even spinal animals can show conditioned leg
withdrawal. Other types of conditioning occur without
forebrain.
• Hypothesis: The forebrain is important in linking
together, by learning, species-typical action patterns
(“fixed action patterns”) which are built in (genetically
determined).
35
Questions, chapter 7
6. What is meant by “stability in time” and
“stability in space”? In which of these is the
forebrain most important?
36
Conclusion: Behavior without forebrain
• Summary in terms of fundamental stabilities
(as expressed by W.J.H. Nauta)
– Stability in space is maintained (at a crude level).
– Stability of the internal mileau is OK, but best if
hypothalamus is left intact.
– Very poor “stability in time”
• Behavior determined by current inputs
• Little or no motivation-initiated behavior
• Little or no long-term memory.
• In addition, without a forebrain a mammal has major losses in sensory and motor acuity
37
X
Decortication, with sparing of corpus striatum
• Compared with decerebrates, cats show more
behavior sequences, e.g., grooming, spontaneous
eating, mating.
• But remember, decerebrate rats show grooming
even without sparing of the striatum.
• Why the species difference?
38
X
Neocortex removals in various species compared
• The greater the amount of neocortex removed, – the longer lasting the resulting defects*,
– and the more likely some of those defects will
be permanent.
• Again, how do we account for these species
differences?
*The “defects”: The immediately noticeable deficiencies in motor
control. Many sensory and cognitive defects occur as well.
39
Questions, chapter 7
7. What, in a simple phrase, is meant by
diaschisis? Describe an example. Why is an
understanding of this phenomenon so
important in the interpretation of species
differences in brain lesion effects?
Next slide
40
“Diaschisis” phenomena
• Term refers to quantitative effects of lesions,
usually large lesions, on the functions of other
structures not directly damaged
• Defined as deafferentation depression
• Example: “spinal shock” in different species
• Next:
– Von Monikow’s “corticospinal diaschisis”
– Recovery phenomena: possible mechanisms
41
Diaschisis: basis
Courtesy of MIT Press. Used with permission.
Schneider, G. E. Brain structure and its Origins: In the Development and in
Evolution of Behavior and the Mind. MIT Press, 2014. ISBN: 9780262026734.
= excitatory connections
42
Corticospinal Diaschisis: concept
Cortex
LESION
Spinal
cord
Courtesy of MIT Press. Used with permission.
Schneider, G. E. Brain structure and its Origins: In the Development and in
Evolution of Behavior and the Mind. MIT Press, 2014. ISBN: 9780262026734.
= excitatory connections
43
Diaschisis: the denervation depression phenomenon
Courtesy of MIT Press. Used with permission.
Schneider, G. E. Brain structure and its Origins: In the Development and in
Evolution of Behavior and the Mind. MIT Press, 2014. ISBN: 9780262026734.
= excitatory connections
Greater deafferentation
(more connections have
been removed)
44
Recovery of excitability after denervation depression • Collateral sprouting
• Denervation supersensitivity
45
Diaschisis: the denervation depression phenomenon
Courtesy of MIT Press. Used with permission.
Schneider, G. E. Brain structure and its Origins: In the Development and in
Evolution of Behavior and the Mind. MIT Press, 2014. ISBN: 9780262026734.
= excitatory connections
Sketch the predicted collateral sprouting. How can one test for
collateral sprouting? Or for denervation supersensitivity?
Greater response to neurotransmitter
46
Conclusion about brain lesion effects
• Brain lesions cannot be considered as mere subtractions of functions of the removed tissue.
• Quantitative effects of lesions have to be considered.
• Now we return to a functional overview of forebrain structures
47
Questions, chapter 7
8. What part of the forebrain is most involved
in the changes that occur during habit
formation, or procedural learning (implicit
learning)?
Next slide
48
Functional overview of forebrain structures, continued:
• Corpus striatum contributions:
– The Bard & Macht study indicates that one aspect may be
the (learned) linking of components of instinctive behavior
patterns during development, as described by Paul
Leyhausen in his behavioral studies of kittens and cats.
– Experimental studies have found that striatum is crucial for
habit formation – “procedural learning” or “implicit
learning”.
– Anatomical connections of the striatum fit these functions.
– Human pathologies of the striatum and its connections raise
many additional issues.
We will return to these issues later.
49
Contributions of forebrain components based on
other studies, both anatomical and functional
 Corpus striatum
•Diencephalon (‘tweenbrain, so named
because it is between the hemispheres of the
endbrain)
• Limbic endbrain
• Neocortex
50
Questions, chapter 7
9. According to the suggestions in this
chapter, what is a reason why sensory
pathways ascending to the forebrain almost
always have a connection in the thalamus?
51
Diencephalon (‘tweenbrain) • Optic inputs were very early
• They play a special role in organizing the daily
rhythm of activity, which is so different during
day and night, and also when light levels vary
during the daytime.
– Hypothalamic and epithalamic afferents from the lateral eyes
and from the parietal eye entrain the endogenous circadian
activity rhythm.
– This rhythm, the biological clock, and these visual inputs,
modulate the behavior of the entire system.
52
Epithalamus and
pineal organ
Hypothalamus (with neurohypophysis
attached), with input from lateral eyes
in primitive chordates
Courtesy of MIT Press. Used with permission.
Schneider, G. E. Brain structure and its Origins: In the Development and in
Evolution of Behavior and the Mind. MIT Press, 2014. ISBN: 9780262026734.
53
Diencephalon, continued:
Hypothalamus & pituitary
• Other system-wide modulations occur via the
endocrine system’s diencephalic component: the
pituitary.
• Widespread modulation of the CNS is
accomplished by the hypothalamus (called by
Sherrington “the head ganglion of the autonomic
nervous system”), which controls major
motivational states in addition to sleep and
waking.
54
Hypothalamic gating/modulation of neuronal activity in thalamus and subthalamus
• Indicated by studies of projections of the hypothalamus • Demonstrated by electrophysiological studies of biting attack behavior by cats (John Flynn and students at Yale, 1960s & 1970s)
– Electrical stimulation of lateral hypothalamus can cause an
altered state: the predator mood.
– Such stimulation also causes changes in neuronal firing
patterns in thalamus and neocortex (as well as elsewhere).
• In the evolution of sensory pathways ascending to the endbrain, this hypothalamic function may have
been a major reason why a connection to thalamus,
rather than more direct pathways, was almost
always retained.
Gating of information flowing to the neocortex
(more on this later)
55
Contributions of forebrain components based on
other studies, both anatomical and functional
 Corpus striatum
 Diencephalon (‘tweenbrain, so named because it is
between the hemispheres of the endbrain)
• Limbic endbrain
• Neocortex
56
Questions, chapter 7
10.The limbic system is characterized by
close interconnections with what portion of
the upper brainstem?
The hypothalamus
57
Some
“Limbic”
connections
(Note definition of limbic system)
Courtesy of MIT Press. Used with permission.
Schneider, G. E. Brain structure and its Origins: In the Development and in
Evolution of Behavior and the Mind. MIT Press, 2014. ISBN: 9780262026734.
58
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9.14 Brain Structure and Its Origins
Spring 2014
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